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binary-analysis-patterns · wshobson-agents · Flowy
Master binary analysis patterns including disassembly, decompilation, control flow analysis, and code pattern recognition. Use when analyzing executables, understanding compiled code, or performing static analysis on binaries.
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Master binary analysis patterns including disassembly, decompilation, control flow analysis, and code pattern recognition. Use when analyzing executables, understanding compiled code, or performing static analysis on binaries. 📦 Ships with wshobson-agents
</> SKILL.md
binary-analysis-patterns.SKILL.md
---
name : binary-analysis-patterns
description : Master binary analysis patterns including disassembly, decompilation, control flow analysis, and code pattern recognition. Use when analyzing executables, understanding compiled code, or performing static analysis on binaries.
---
# Binary Analysis Patterns
Comprehensive patterns and techniques for analyzing compiled binaries, understanding assembly code, and reconstructing program logic.
## When to Use This Skill
- Reverse-engineering an unknown executable to understand its behavior
- Analyzing malware or obfuscated binaries with Ghidra / IDA Pro / Binary Ninja
- Recognizing common assembly idioms (function prologues, switch tables, vtable dispatch)
- Reconstructing high-level control flow from compiled code
- Identifying compiler-introduced patterns (stack canaries, PIC trampolines)
## Detailed section: Disassembly Fundamentals
Originally a 2047-byte section in this SKILL.md. Moved to `references/details.md` to fit Codex's 8 KB skill body cap.
## Control Flow Patterns
### Conditional Branches
```asm
; if (a == b)
cmp eax, ebx
jne skip_block
; ... if body ...
skip_block:
; if (a < b) - signed
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cmp eax, ebx
jge skip_block ; Jump if greater or equal
; ... if body ...
skip_block:
; if (a < b) - unsigned
cmp eax, ebx
jae skip_block ; Jump if above or equal
; ... if body ...
skip_block:
```
### Loop Patterns
```asm
; for (int i = 0; i < n; i++)
xor ecx, ecx ; i = 0
loop_start:
cmp ecx, [n] ; i < n
jge loop_end
; ... loop body ...
inc ecx ; i++
jmp loop_start
loop_end:
; while (condition)
jmp loop_check
loop_body:
; ... body ...
loop_check:
cmp eax, ebx
jl loop_body
; do-while
loop_body:
; ... body ...
cmp eax, ebx
jl loop_body
```
### Switch Statement Patterns
```asm
; Jump table pattern
mov eax, [switch_var]
cmp eax, max_case
ja default_case
jmp [jump_table + eax*8]
; Sequential comparison (small switch)
cmp eax, 1
je case_1
cmp eax, 2
je case_2
cmp eax, 3
je case_3
jmp default_case
```
## Data Structure Patterns
### Array Access
```asm
; array[i] - 4-byte elements
mov eax, [rbx + rcx*4] ; rbx=base, rcx=index
; array[i] - 8-byte elements
mov rax, [rbx + rcx*8]
; Multi-dimensional array[i][j]
; arr[i][j] = base + (i * cols + j) * element_size
imul eax, [cols]
add eax, [j]
mov edx, [rbx + rax*4]
```
### Structure Access
```c
struct Example {
int a; // offset 0
char b; // offset 4
// padding // offset 5-7
long c; // offset 8
short d; // offset 16
};
```
```asm
; Accessing struct fields
mov rdi, [struct_ptr]
mov eax, [rdi] ; s->a (offset 0)
movzx eax, byte [rdi+4] ; s->b (offset 4)
mov rax, [rdi+8] ; s->c (offset 8)
movzx eax, word [rdi+16] ; s->d (offset 16)
```
### Linked List Traversal
```asm
; while (node != NULL)
list_loop:
test rdi, rdi ; node == NULL?
jz list_done
; ... process node ...
mov rdi, [rdi+8] ; node = node->next (assuming next at offset 8)
jmp list_loop
list_done:
```
## Common Code Patterns
### String Operations
```asm
; strlen pattern
xor ecx, ecx
strlen_loop:
cmp byte [rdi + rcx], 0
je strlen_done
inc ecx
jmp strlen_loop
strlen_done:
; ecx contains length
; strcpy pattern
strcpy_loop:
mov al, [rsi]
mov [rdi], al
test al, al
jz strcpy_done
inc rsi
inc rdi
jmp strcpy_loop
strcpy_done:
; memcpy using rep movsb
mov rdi, dest
mov rsi, src
mov rcx, count
rep movsb
```
### Arithmetic Patterns
```asm
; Multiplication by constant
; x * 3
lea eax, [rax + rax*2]
; x * 5
lea eax, [rax + rax*4]
; x * 10
lea eax, [rax + rax*4] ; x * 5
add eax, eax ; * 2
; Division by power of 2 (signed)
mov eax, [x]
cdq ; Sign extend to EDX:EAX
and edx, 7 ; For divide by 8
add eax, edx ; Adjust for negative
sar eax, 3 ; Arithmetic shift right
; Modulo power of 2
and eax, 7 ; x % 8
```
### Bit Manipulation
```asm
; Test specific bit
test eax, 0x80 ; Test bit 7
jnz bit_set
; Set bit
or eax, 0x10 ; Set bit 4
; Clear bit
and eax, ~0x10 ; Clear bit 4
; Toggle bit
xor eax, 0x10 ; Toggle bit 4
; Count leading zeros
bsr eax, ecx ; Bit scan reverse
xor eax, 31 ; Convert to leading zeros
; Population count (popcnt)
popcnt eax, ecx ; Count set bits
```
## Decompilation Patterns
### Variable Recovery
```asm
; Local variable at rbp-8
mov qword [rbp-8], rax ; Store to local
mov rax, [rbp-8] ; Load from local
; Stack-allocated array
lea rax, [rbp-0x40] ; Array starts at rbp-0x40
mov [rax], edx ; array[0] = value
mov [rax+4], ecx ; array[1] = value
```
### Function Signature Recovery
```asm
; Identify parameters by register usage
func:
; rdi used as first param (System V)
mov [rbp-8], rdi ; Save param to local
; rsi used as second param
mov [rbp-16], rsi
; Identify return by RAX at end
mov rax, [result]
ret
```
### Type Recovery
```asm
; 1-byte operations suggest char/bool
movzx eax, byte [rdi] ; Zero-extend byte
movsx eax, byte [rdi] ; Sign-extend byte
; 2-byte operations suggest short
movzx eax, word [rdi]
movsx eax, word [rdi]
; 4-byte operations suggest int/float
mov eax, [rdi]
movss xmm0, [rdi] ; Float
; 8-byte operations suggest long/double/pointer
mov rax, [rdi]
movsd xmm0, [rdi] ; Double
```
## Ghidra Analysis Tips
### Improving Decompilation
```java
// In Ghidra scripting
// Fix function signature
Function func = getFunctionAt(toAddr(0x401000));
func.setReturnType(IntegerDataType.dataType, SourceType.USER_DEFINED);
// Create structure type
StructureDataType struct = new StructureDataType("MyStruct", 0);
struct.add(IntegerDataType.dataType, "field_a", null);
struct.add(PointerDataType.dataType, "next", null);
// Apply to memory
createData(toAddr(0x601000), struct);
```
### Pattern Matching Scripts
```python
# Find all calls to dangerous functions
for func in currentProgram.getFunctionManager().getFunctions(True):
for ref in getReferencesTo(func.getEntryPoint()):
if func.getName() in ["strcpy", "sprintf", "gets"]:
print(f"Dangerous call at {ref.getFromAddress()}")
```
## IDA Pro Patterns
### IDAPython Analysis
```python
import idaapi
import idautils
import idc
# Find all function calls
def find_calls(func_name):
for func_ea in idautils.Functions():
for head in idautils.Heads(func_ea, idc.find_func_end(func_ea)):
if idc.print_insn_mnem(head) == "call":
target = idc.get_operand_value(head, 0)
if idc.get_func_name(target) == func_name:
print(f"Call to {func_name} at {hex(head)}")
# Rename functions based on strings
def auto_rename():
for s in idautils.Strings():
for xref in idautils.XrefsTo(s.ea):
func = idaapi.get_func(xref.frm)
if func and "sub_" in idc.get_func_name(func.start_ea):
# Use string as hint for naming
pass
```
## Best Practices
### Analysis Workflow
1. **Initial triage**: File type, architecture, imports/exports
2. **String analysis**: Identify interesting strings, error messages
3. **Function identification**: Entry points, exports, cross-references
4. **Control flow mapping**: Understand program structure
5. **Data structure recovery**: Identify structs, arrays, globals
6. **Algorithm identification**: Crypto, hashing, compression
7. **Documentation**: Comments, renamed symbols, type definitions
### Common Pitfalls
- **Optimizer artifacts**: Code may not match source structure
- **Inline functions**: Functions may be expanded inline
- **Tail call optimization**: `jmp` instead of `call` + `ret`
- **Dead code**: Unreachable code from optimization
- **Position-independent code**: RIP-relative addressing
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